Uwe Raabe write in
https://translate.google.com/translate?hl=en&sl=de&u=https://www.delphipraxis.net/186612-32-bit-tstringlist-textdatei-mit-30mio-zeilen-3.html&prev=search&pto=aue
The storage space for a string is limited to 2 GB even under 64 bit, which corresponds to approx. 2 ^ 30 characters. Since when loading, as well as when accessing .Text, the entire content is messed up as a string, a natural limit has been reached here. The StringList could probably hold even more data under 64 bit, but then it must be added line by line with Add. Everything that regards the content as a single string (Load, Save, Text, ???) must then not be used.
Look this link:
https://stackoverflow.com/questions/27007904/tstringlist-loadfromfile-exceptions-with-large-text-files